Field of the Invention
This disclosure relates to a composite plastic lens in which a resin lens and a resin light-shielding holder are integrated, and a method of manufacturing the same.
Description of the Related Art
The resin lens is used in a wide range of fields such as photographing lenses used in digital cameras or video cameras, recording and reproducing pickup lenses for optical discs, projecting lenses used in projectors. Many of these resin lenses are formed by injection molding for reducing costs. However, in order to cause the resin lens to function in a state of being assembled with a product as a part, the lens may be put into a frame-shaped holder and integrated therewith in a post process. The frame-shaped holder is expressed by terms such as a lens barrel and a lens holder. In this disclosure, a term “holder” is used throughout. In many cases, a gripping portion to be operated in conjunction with an operating portion and a light-shielding portion that limits a light effective area are additionally formed on the holder.
In order to respond requirements such as a reduction in cost and a reduction in weight, the holders used in recent years are made of a resin, and an adhesive agent is generally used for fixing and integrating the holder with the resin lenses. However, for those requiring high degree of positioning accuracy between the lens and holder, the integration with high degree of accuracy is difficult with the adhesive agent. In order to solve the above-described problem, an insert molding technology configured to achieve integration by molding a resin lens in a state in which a resin holder is inserted into a metal mold is disclosed in Japanese Patent Laid-Open NO. 2002-148501. In Japanese Patent Laid-Open NO. 2004-319347, a configuration in which a resin holder inserted into a metal mold at the time of lens formation is held at a predetermined position further reliably is disclosed.
However, the composite mold articles disclosed in the above-described Japanese Patent Laid-Open NO. 2002-148501 and Japanese Patent Laid-Open NO. 2004-319347 each have a problem to be solved.
The configuration of Japanese Patent Laid-Open NO. 2002-148501 has a problem that if a lens resin is injected into a metal mold in a state in which a resin holder is inserted, a colored holder resin fuses and transfers into a transparent lens resin by heat and a shearing force of the lens resin and hence the appearance of the lens is degraded.
In order to solve this problem, in Japanese Patent Laid-Open NO. 2004-319347, occurrence of appearance defects is suppressed by providing a protrusion on a core of a metal mold in which a resin holder is to be inserted so as to hold the holder at a predetermined position by the protrusion even when being subjected to heat and a shearing force during the lens resin is being injected.
However, in a first embodiment of the Japanese Patent Laid-Open NO. 2004-319347, if the injection speed of the lens resin is lowered at the time of lens formation, the time period in which the holder is subjected to heat and a shearing force is increased, so that the colored holder resin cannot be suppressed from fusing and transferring into the transparent lens resin. In particular, the temperature of the lens resin is high, and hence this problem is specifically notable in the vicinity of a gate portion at which the temperature of the resin is high, and which is subjected to a holding pressure. Therefore, there is a problem that the molding conditions are limited at the time of the lens formation.
In a configuration in the embodiment of the Japanese Patent Laid-Open NO. 2004-319347, the holder is embedded around the protrusion of a core, which helps the positioning of insertion of the holder, and if the lens is formed in this state, a level difference of the embedment is transferred to a peripheral portion of the lens. If a ridge caused by the level difference exists on the lens, a problem of ghost caused by a reflection of incident light, which is unexpected in the specification of the lens, may occur.
This disclosure provides a composite plastic lens which prevents a resin light-shielding holder from fusing and transferring into a resin lens and reduces a probability of occurrence of ghost, and a method of manufacturing the composite plastic lens.